1. Technical Field
The present invention relates to a brake mechanism used in a motor vehicle of a type equipped with a radial flow compressor connected to the crankshaft of the engine for exerting a braking force against the crankshaft using the air compressing work of the compressor as the braking force. More particularly, it relates to a brake mechanism in which resonating vibration is prevented in the radial compressor at its impeller and impeller shaft.
2. Background Art
Numerous arrangements are known in the art which function as a power recovery turbine, including a construction in which an impeller is attached to only one end of the output shaft or the crankshaft of the engine, as is disclosed in Japanese Patent Application No. 62-136474 (1987), entitled "Turbine Brake Mechanism."
In the Japanese patent application mentioned above, and as is illustrated in FIG. 2 of the accompanying drawings, a radial compressor c is connected to one end of the crankshaft b of the engine a. The compressor c is driven by the shaft b and compresses and delivers a gas it has sucked in. In other words, the radial compressor c consumes energy from the engine, thereby braking the engine and thus the vehicle. The gas may be either external air or exhaust gas.
In another proposed power recovery turbine arrangement, a turbine is provided in the exhaust line in such a way that the turbine shaft is connected with an engine crankshaft via a gear train so as to effectively recover the energy of the exhaust gas.
In the latter mentioned arrangement, only one impeller is attached to an end of the impeller shaft. This means that the distance from the center of gravity of the impeller to the point of rotational support of the impeller shaft (called "overhang") is necessarily long. Structurally speaking, this arrangement is in contrast to a turbocharger, where a pair of impellers (a turbine and a blower) are attached to either end of a common rotating shaft, the shaft being supported at each of its ends.
One problem of the above-mentioned structure having a large overhang is that the system's resonant frequency is low due to the imbalance couple that is inevitably present; namely, such a rotation system is liable to undergo resonating vibration at a low frequency corresponding to a low engine revolution speed within the ordinary service range. Even though this difficulty can be overcome by employing a longer impeller shaft, since the longer the shaft, the higher the resonant frequency, such a solution entails undesirable elongation of the total dimension of the impeller system, i.e. the distance between the impeller tip to the rear end of the impeller shaft becomes longer.